Apparatus and method for using checking instructions in a floating-point execution unit

Abstract

The use of checking instructions to detect special and exceptional cases of a defined data format in a microprocessor is disclosed. Generally speaking, a checking instruction is included with the microcode of floating-point instructions to detect special and exceptional cases of operand values for the floating-point instructions. A checking instruction is configured to set one or more flags in a flags register if it detects a special or exceptional case for an operand value. A checking instruction may also set the result or results of a floating-point instruction to a result value if a special or exceptional case is detected. In addition, a checking instruction may be configured to set one or more bits in status register if a special or exceptional case is detected. After a checking instruction completes execution, a subsequent microcode instruction can be executed to determine if one or more flags were set by the checking instruction. If one or more flags have been set by the checking instruction, the subsequent microcode instruction can branch to a non-sequential microcode instruction to handle the special or exceptional case detected by the checking instruction.

Description

1. Field of the InventionThis invention relates generally to the field of microprocessors and, more particularly, to floating-point execution units within microprocessors.2. Description of the Related ArtMicroprocessors are typically designed with a number of "execution units" that are each optimized to perform a particular set of functions or instructions. For example, one or more execution units within a microprocessor may be optimized to perform memory accesses, i.e., load and store operations. Other execution units may be optimized to perform general arithmetic and logic functions, e.g., shifts and compares. Many microprocessors also have specialized execution units configured to perform more complex floating-point arithmetic operations including multiplication and reciprocal operations. These specialized execution units typically comprise hardware that is optimized to perform one or more floating-point arithmetic functions.Most microprocessors must support multiple data types. ...

AI Technical Summary

Problems solved by technology

Detecting and handling special and exceptional cases, however, generally requires additional microprocessor resources and produces undesirable execution latencies.

Furthermore, checking instructions may reduce the amount of constant ROM storage required to hold the possible results of special and exceptional cases.

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